Reversible Magnetism between an Antiferromagnet and a

Aug 11, 2010 - In addition, in the case of partially desolvated crystals that have mixed domains of ferromagnetically and antiferromagnetically ordere...
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Reversible Magnetism between an Antiferromagnet and a Ferromagnet Related to Solvation/Desolvation in a Robust Layered [Ru2]2TCNQ Charge-Transfer System Natsuko Motokawa,† Satoshi Matsunaga,†,§ Shinya Takaishi,† Hitoshi Miyasaka,*,† Masahiro Yamashita,† and Kim R. Dunbar‡ Department of Chemistry, Graduate School of Science, Tohoku UniVersity, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan, and Department of Chemistry, Texas A&M UniVersity, P.O. Box 30012, College Station, Texas 77842-3012 Received March 22, 2010; E-mail: [email protected]

Abstract: The charge-transfer compound [{Ru2(O2CPh-o-Cl)4}2TCNQ(MeO)2] · CH2Cl2 (1; o-ClPhCO2- ) o-chlorobenzoate; TCNQ(MeO)2 ) 2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane) was synthesized from the reaction of the neutral precursors [Ru2II,II(O2CPh-o-Cl)4] (abbreviated as [Ru2II,II] or [Ru24+]) and TCNQ(MeO)2 in a CH2Cl2/nitrobenzene solution. The structure consists of two-dimensional layers consisting of an infinite array in which [Ru2II,II] units are involved in charge transfer to TCNQ(MeO)2 to give a formal charge of [{Ru24.5+}-TCNQ(MeO)2• --{Ru24.5+}]. Interstitial CH2Cl2 molecules are located in the void spaces between the layers. Strong intralayer magnetic coupling between the units [Ru2II,II] with S ) 1 or [Ru2II,III] with S ) 3/2 and TCNQ(MeO)2• - with S ) 1/2, as well as long-range ordering due to antiferromagnetic interlayer interactions, was observed. An antiferromagnetic ground state exists below TN ) 75 K, which undergoes a metamagnetic transition under applied fields less than 2 T to a field-induced canted antiferromagnetic state with large coercivities up to Hc ) 1.6 T at 1.8 K. Compound 1 gradually loses the interstitial CH2Cl2 molecule at room temperature to form a dried sample (1-dry) without loss of crystallinity and converts nearly reversibly back to 1 after being exposed to CH2Cl2 vapor for 72 h (distinguished as 1′). Interestingly, during this process there is no significant change in lattice dimensions and bond distances or angles with a volume change of only 1.2 vol %. The only discernible difference is ordering/disordering of a pendant ligand orientation, but the magnetism is dramatically altered to a ferromagnetic state with Tc ≈ 56 K for 1-dry. The magnetic property changes are gradual and depend on the degree of interstitial CH2Cl2 molecule loss with reversibility in the process of going between 1 and 1-dry. In addition, in the case of partially desolvated crystals that have mixed domains of ferromagnetically and antiferromagnetically ordered domains for desolvated and solvated segments, respectively, the complete change to ferromagnet can also be triggered by magnetic fields even if the desolvated segments are comparatively minor compared to the solvated segments in a crystal. Surprisingly, the information of the existence of ferromagnetically ordered domains is dynamically recorded in the entire crystal after applying significant magnetic fields as if the majority of the antiferromagnetically ordered domains for solvated segments were never present.

Introduction

Flexible molecular magnets that undergo a reversible change of their magnetic properties in response to external modulations such as light,1 pressure,2 electrical field,3 humidity,4 solvation/ desolvation,5 or molecular guest absorption/desorption6 are one of the recent challenging targets in the field of molecular magnetism. With the exception of cases in which the spin state or electronic state of magnetic centers are directly modified by spin-crossover7 and/or intramolecular charge transfer,1,8 for example, most instances of magnetic changes are accompanied by significant structural changes that strongly affect bondmediating magnetic paths or through-space interactions. Reversible structural changes with concomitant changes in magnetism †

Tohoku University. Texas A&M University. § Current address: Department of Chemistry, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan. ‡

10.1021/ja102412g  2010 American Chemical Society

can be divided into four categories: (i) bond cleavage or bond formation, (ii) deformations of the lattice (lattice sliding, contracting/expanding, etc.), (iii) collapse/regeneration of lattice, or (iv) a combination of the first three processes. These changes occur either in a crystal-to-crystal phase or a crystal-toamorphous phase transformation. A particularly notable example (1) (a) Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Science 1996, 272, 704. (b) Ohkoshi, S.; Hashimoto, K. J. Am. Chem. Soc. 1999, 121, 10591. (c) Arimoto, Y.; Ohkoshi, S.; Zhong, Z. J.; Seino, H.; Mizobe, Y.; Hashimoto, K. J. Am. Chem. Soc. 2003, 125, 9240. (d) Hozumi, T.; Hashimoto, K.; Ohkoshi, S. J. Am. Chem. Soc. 2005, 127, 3864. (e) Ohkoshi, S.; Tokoro, H.; Hozumi, T.; Zhang, Y.; Hashimoto, K.; Mathonie´re, C.; Bord, I.; Rombaut, G.; Verelst, M.; Cartier dit Moulin, C.; Villain, F. J. Am. Chem. Soc. 2006, 128, 270. (f) Ohkoshi, S.; Hamada, Y.; Matsuda, T.; Tsunobuchi, Y.; Tokoro, H. Chem. Mater. 2008, 20, 3048. (g) Tokoro, H.; Matsuda, T.; Nuida, T.; Moritomo, Y.; Ohoyama, K.; Dangui, E. D. L.; Boukheddaden, K.; Ohkoshi, S. Chem. Mater. 2008, 20, 423. (h) Ohkoshi, S.; Hamada, Y.; Matsuda, T.; Tsunobuchi, Y.; Tokoro, H. Chem. Mater. 2008, 20, 3048. J. AM. CHEM. SOC. 2010, 132, 11943–11951

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of such behavior was reported by Veciana et al., who observed a reversible solvent-induced “shrinking-breathing” process in a crystal of CuII-radical nonoporous magnetic material involving large volume changes of >30 vol % that strongly influence the magnetic properties.5b Such materials were dubbed “magnetic sponges” by Kahn et al. many years ago.5a Also of relevance is the discovery by Kurmoo et al., who reported a minimal change of framework geometry of ca. 0.5 vol % of a nanoporous material, [CoII3(OH)2(C4O4)2] · 3H2O, effected by the loss of water molecules with heating up to ca. 200 °C that induces a drastic magnetic change from ferromagnetic/antiferromagnetic at temperatures between 6 and 8 K.5d These magnetic changes are attributed to the presence or loss of hydrogen bonding related to interstitial water molecules that mediate weak antiferromagnetic exchange interactions between the ferromagnetic sublattices. Another recent example of solvent-induced magnetic properties is the report by Dunbar et al., where removal of methanol molecules from the interstices of a metal-organic framework based on a two-dimensional (2D) hexagonal MnIITCNQF4 net (TCNQF4 ) 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) results in a conversion from weak antiferromagnetic to ferromagnetic coupling, which leads to the formation of a glassy magnet; the magnetic behavior can be reversibly cycled between the solvated and desolvated forms of the material by heating and immersion in methanol.5g Herein we report a new 2D layered compound, [{Ru2(O2CPho-Cl)4}2TCNQ(OMe)2] · CH2Cl2 (1), composed of a 2:1 ratio of (2) (a) Coronado, E.; Gime´nez-Lo´pez, M. C.; Levchenko, G.; Romero, F. M.; Garcı´a-Baonza, V.; Milner, A.; Paz-Pasternak, M. J. Am. Chem. Soc. 2005, 127, 4580. (b) Egan, L.; Kamenev, K.; Papanikolaou, D.; Takabayashi, Y.; Margadonna, S. J. Am. Chem. Soc. 2006, 128, 6034. (c) Ohba, M.; Kaneko, W.; Kitagawa, S.; Maeda, T.; Mito, M. J. Am. Chem. Soc. 2008, 130, 4475. (3) Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Science 1996, 271, 49. (4) Ohkoshi, S.; Arai, K.; Sato, Y.; Hashimoto, K. Nat. Mater. 2004, 3, 857. (5) (a) Larionova, J.; Chavan, S. A.; Yakhmi, J. V.; Frøystein, A. G.; Sletten, J.; Sourisseau, C.; Kahn, O. Inorg. Chem. 1997, 36, 6374. (b) Maspoch, D.; Ruiz-Molina, D.; Wurst, K.; Domingo, N.; Cavallini, M.; Biscarini, F.; Tejada, J.; Rovira, C.; Veciana, J. Nat. Mater. 2003, 2, 190. (c) Kurmoo, M.; Kumagai, H.; Hughes, S. M.; Kepert, C. J. Inorg. Chem. 2003, 42, 6709. (d) Kurmoo, M.; Kumagai, H.; Chapman, K. W.; Kepert, C. J. Chem. Commun. 2005, 3012. (e) Yanai, N.; Kaneko, W.; Yoneda, K.; Ohba, M.; Kitagawa, S. J. Am. Chem. Soc. 2007, 129, 3496. (f) Milon, J.; Daniel, M.-C.; Kaiba, A.; Guionneau, P.; Brande´s, S.; Sutter, J.-P. J. Am. Chem. Soc. 2007, 129, 13872. (g) Lopez, N.; Zhao, H.; Prosvirin, A. V.; Chouai, A.; Shatruk, M.; Dunbar, K. R. Chem. Commun. 2007, 4611. (h) Cheng, X.-N.; Zhang, W.-X.; Chen, X.-M. J. Am. Chem. Soc. 2007, 129, 15738. (i) Ohkoshi, S.; Tsunobuchi, Y.; Takahashi, H.; Hozumi, T.; Shiro, M.; Hashimoto, K. J. Am. Chem. Soc. 2007, 129, 3084. (j) Zhang, Y.-J.; Liu, T.; Kanegawa, S.; Sato, O. J. Am. Chem. Soc. 2009, 131, 7942. (k) Duan, Z.; Zhang, Y.; Zhang, B.; Zhu, D. J. Am. Chem. Soc. 2009, 131, 6934. (6) (a) Kaneko, W.; Ohba, M.; Kitagawa, S. J. Am. Chem. Soc. 2007, 129, 13706. (b) Ghosh, S. K.; Kaneko, W.; Kiriya, D.; Ohba, M.; Kitagawa, S. Angew. Chem., Int. Ed. 2008, 47, 8843. (7) (a) Kosaka, W.; Nomura, K.; Hashimoto, K.; Ohkoshi, S. J. Am. Chem. Soc. 2005, 127, 8590. (b) Nihei, M.; Han, L.; Oshio, H. J. Am. Chem. Soc. 2007, 129, 5312. (c) Neville, S. M.; Halder, G. J.; Chapman, K. W.; Duriska, M. B.; Southon, P. D.; Cashion, J. D.; Le´tard, J.-F.; Moubaraki, B.; Murray, K. S.; Kepert, C. J. J. Am. Chem. Soc. 2008, 130, 2869. (d) Ohba, M.; Yoneda, K.; Agustı´, G.; Mun˜oz, M. C.; Gaspar, A. B.; Real, J. A.; Yamasaki, M.; Ando, H.; Nakao, Y.; Sakaki, S.; Kitagawa, S. Angew. Chem., Int. Ed. 2009, 48, 4767. (e) Neville, S. M.; Halder, G. J.; Chapman, K. W.; Duriska, M. B.; Moubaraki, B.; Murray, K. S.; Kepert, C. J. J. Am. Chem. Soc. 2009, 131, 12106. (8) (a) Shimamoto, N.; Ohkoshi, S.; Sato, O.; Hamshimoto, K. Inorg. Chem. 2002, 41, 678. (b) Tokoro, H.; Ohkoshi, S.; Matsuda, T.; Hashimoto, K. Inorg. Chem. 2004, 43, 5231. (c) Ohkoshi, S.; Matsuda, T.; Tokoro, H.; Hashimoto, K. Chem. Mater. 2005, 17, 81. (d) Ohkoshi, S.; Ikeda, S.; Hozumi, T.; Kashiwagi, T.; Hashimoto, K. J. Am. Chem. Soc. 2006, 128, 5320. 11944

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the paddlewheel diruthenium unit [Ru2II,II(O2CPh-o-Cl)4] (oClPhCO2- ) o-chlorobenzoate) and 2,5-dimethoxy-7,7,8,8tetracyanoquinodimethane (TCNQ(MeO)2) and one molecule of CH2Cl2 located between layers. Reversible magnetism between antiferromagnetic and ferromagnetic is extremely sensitive to the solvation/desolvation of the crystallization solvent (CH2Cl2) at room temperature. This material is different from the aforementioned cases in that the gradual magnetic change occurs without significant lattice deformation or magnetic path cleavage or path formation of hydrogen bonds but is instead associated with slight structural fluctuations caused by the ordering/ disordering of ligand orientation driven by the fix-and-release of the CH2Cl2 molecules acting as a clip. In the case of partially desolvated crystals that have mixed domains of ferromagnetically and antiferromagnetically ordered domains for desolvated and solvated segments, respectively, the complete change to a ferromagnet can also be triggered by magnetic fields even if the desolvated segments are minor as compared to the solvated segments in a crystal. Surprisingly, the information of the existence of ferromagnetically ordered domains is dynamically recorded in the entire crystal after applying significant magnetic fields as if the majority of the antiferromagnetically ordered domains were never present. Results and Discussion

Compound 1 was prepared by a slow diffusion reaction of [Ru2(O2CPh-o-Cl)4(THF)2]9 in CH2Cl2 (bottom layer) and TCNQ(OMe)2 in nitrobenzene (top layer) under an ultrapure N2 atmosphere. Dark-green block-shaped crystals of 1 were obtained, which crystallized in the triclinic space group P-1 (Z ) 1). There are two different [Ru2] units, [Ru(1)2] and [Ru(2)2], and one TCNQ(OMe)2 molecule in the formula unit (Figure 1a) with the [Ru2] units and TCNQ(MeO)2 being situated on inversion centers at the midpoint of the Ru-Ru bond and the quinonoid ring of TCNQ(MeO)2, where only [Ru(2)2] has a positional disorder in its o-ClPh groups (vide infra). The [Ru2] and TCNQ(MeO)2 units act as a linear-coordination acceptor and a µ4-bridging ligand (coordination-donor), respectively, the result of which is a fishnet-like hexagonal 2D network (Figure 1b). Relevant metrical parameters are Ru-NtC [Ru(1)-N(1) ) 2.221(3) Å, Ru(2)-N(2) ) 2.236(3) Å, Ru(1)-N(1)-C(29) ) 160.6(3)°, Ru(2)-N(2)-C(31) ) 165.2(3)°] (Table 1). The interlayer distance, defined as the distance between the leastsquares planes of the 2D sheets, is 8.367 Å. One CH2Cl2 molecule of crystallization is located between the layers (Figure 1c). The oxidation state of the molecules in the extended structure can be roughly estimated from characteristic bonds. For the [Ru2] unit, Ru-Oeq (Oeq ) carboxylate oxygen) distances reflect the valence of [Ru2] unit; for comparison sake, we note that average values for [Ru2II,II(O2CPh-o-Cl)4(THF)2] · 2THF and [Ru2II,III(O2CPh-o-Cl)4(THF)2]BF4 · THF are 2.065 and 2.019 Å, respectively (Table S1 and Figure S1 in Supporting Information).9 The average corresponding distances in 1 are 2.036 and 2.044 Å for the [Ru(1)2] and [Ru(2)2] units, respectively, values that are intermediate between those for [Ru2II,II] and [Ru2II,III]. These data are an indication of the occurrence of charge transfer to TCNQ(MeO)2 with the result formally being [Ru24.5+] units. (9) The starting material for 1, [Ru2II,II(O2CPh-o-Cl)4(THF)2] · 2THF, and its oxidized material, [Ru2II,III(O2CPh-o-Cl)4(THF)2]BF4 · THF, were synthesized following general methods reported previously and crystallographically characterized (Table S1 and Figure S1 in Supporting Information and CCDC-770525 and 770524, respectively).

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Figure 1. Thermal ellipsoid plots of the formula unit of 1 (a) and 1-dry (d) (50% probability ellipsoids; symmetry operations (*) 1 - x, 2 - y, -z; (**)

2 - x, 1 - y, 1 - z; (***) 2 - x, 1 - y, -z), where disordered Cl atoms of the [Ru2] moiety are represented by dashed bonds, and packing diagrams are projected along the a axis (b) and (e) and the [1-10] direction (c) and (f) for 1 and 1-dry, respectively. The CH2Cl2 molecules in 1 are represented by a yellow CPK model. Hydrogen atoms are omitted for the sake of clarity.

The bond distances in TCNQ(MeO)2 are also sensitive to the charge that varies from the quinonoid (neutral) form with TCNQ(MeO)20 to the benzenoid (ionic) form with TCNQ(MeO)2• -. The charge was estimated on the basis of the Kistenmacher relationship F ) A[c/(b + d)] + B with AH ) -41.667 and BH ) 19.833 for the original TCNQ,10 where b, c, and d are respective bond distances for 7,9-, 1,7-, and 1,2positioned C-C sets in the TCNQ(MeO)2 moiety of 1 (see Table 1).11 The estimated F value for 1 is -1.50, which in accord with a charge balance of [{Ru24.5+}-TCNQ(MeO)2• --{Ru24.5+}] (10) Kintenmacher, T. J.; Emge, T. J.; Bloch, A. N.; Cowan, D. O. Acta Crystallogr., Sect. B 1982, 38, 1193. (11) Miyasaka, H.; Campos-Ferna´ndez, C. S.; Cle´rac, R.; Dunbar, K. R. Angew. Chem., Int. Ed. 2000, 39, 3831.

as reported previously for [{Ru2(O2CCF3)4}2TCNQF4] · 3(pxylene) (CF3CO2- ) trifluoroacetonate, TCNQF4 ) 2,3,5,6tetrafluoro-7,7,8,8-tetracyanoquinodimethane).12 IR data for 1 also support the assignment of the oxidation state. The ν(CtN) modes for TCNQ(MeO)2 appear at 2193, 2157, and 2106 cm-1 for 1, which supports the assignment of the radical anion form of the TCNQ(OMe)2 moiety because of significant red-shifting as compared to neutral TCNQ(OMe)20

(12) (a) Miyasaka, H.; Izawa, T.; Takahashi, N.; Yamashita, M.; Dunbar, K. R. J. Am. Chem. Soc. 2006, 128, 11358. (b) Miyasaka, H.; Motokawa, N.; Matsunaga, S.; Yamashita, M.; Sugimoto, K.; Mori, T.; Toyota, N.; Dunbar, K. R. J. Am. Chem. Soc. 2010, 132, 1532. J. AM. CHEM. SOC.

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Table 1. Important Bond Distances and Angles for 1, 1-dry, and 1′

Figure 2. Visualization of the variation in the formula unit via the process

of desolvation/solvation (from left, 1, 1-dry, and 1′), in which dashed circles indicate an order/disorder in the o-ClPh group of the [Ru(1)2] moiety concomitant with changes in solvation.

1

1-dry

Ru(1)-Ru(1) Ru(2)-Ru(2) Ru(1)-O(1) Ru(1)-O(2) Ru(1)-O(3) Ru(1)-O(4) Ru(2)-O(5) Ru(2)-O(6) Ru(2)-O(7) Ru(2)-O(8) Ru(1)-N(1) Ru(2)-N(2) a1, a2 b1, b2 c d1, d2 e

Distances (Å) 2.2778(4) 2.2723(5) 2.2835(4) 2.2796(4) 2.020(3) 2.019(3) 2.042(3) 2.037(3) 2.037(3) 2.025(3) 2.043(3) 2.034(3) 2.043(3) 2.037(3) 2.040(3) 2.033(3) 2.040(3) 2.040(3) 2.054(3) 2.046(3) 2.221(3) 2.207(4) 2.236(3) 2.225(4) 1.157(5), 1.150(5) 1.148(6), 1.136(6) 1.395(5), 1.410(5) 1.410(6), 1.407(7) 1.441(5) 1.430(7) 1.410(5), 1.413(5) 1.408(7), 1.419(6) 1.382(6) 1.373(7)

Ru(1)-Ru(1)-N Ru(2)-Ru(2)-N Ru(1)-N(1)-C(29) Ru(2)-N(2)-C(31)

177.40(10) 175.69(9) 160.6(3) 165.2(3)

Angles (deg) 175.86(11) 174.80(11) 161.1(4) 161.9(4)

1′

2.2750(4) 2.2812(4) 2.021(3) 2.041(3) 2.035(3) 2.045(3) 2.040(3) 2.044(3) 2.040(3) 2.049(3) 2.214(3) 2.235(3) 1.158(5), 1.138(6) 1.395(6), 1.406(6) 1.455(6) 1.405(6),1.400(6) 1.388(6) 177.38(10) 175.72(19) 161.1(3) 165.4(3)

(2219 cm-1). As a point of reference, the IR stretches in the ν(CtN) region for LiTCNQ(OMe)2 are located at 2196 and 2173 cm-1. Compound 1 gradually releases CH2Cl2 molecules at room temperature under a N2 atmosphere without loss of crystallinity to form a stable CH2Cl2-free compound (1-dry) after 24 h or more (1-dry can also be obtained by heating at 150 °C for 30 min but would have many more defects than samples prepared at ambient temperatures). Remarkably, single-crystal X-ray analysis of 1-dry (Figure 1d-f) revealed no significant changes in lattice dimensions and a volume change of 1.2 vol % (see Experimental Section). The only notable change is a disorder in the orientation of two o-ClPh groups of the [Ru(1)2] moiety (Table 1 and Figure 2).13 This order/disorder of the o-ClPh groups appears to be a key element in dictating the magnetic modifications (vide infra). Furthermore, 1-dry absorbs CH2Cl2 reversibly to revert with near completion back to the original compound 1 after being exposed to CH2Cl2 vapor for 72 h (distinguished as 1′).14 Compound 1′ was also crystallographi(13) The average Ru-Oeq distances for [Ru(1)2] and [Ru(2)2] in 1-dry are 2.029 and 2.039 Å, which correspond to the quasi-[Ru24.5+] state as well as 1. The r value of TCNQ(MeO)2 for 1-dry estimated using the Kistenmacher relationship is -1.28. (14) The average Ru-Oeq distances for [Ru(1)2] and [Ru(2)2] in 1′ are 2.036 and 2.043 Å, which correspond to the quasi-[Ru24.5+] state as well as 1. The F value of TCNQ(MeO)2 for 1′ is -1.80. 11946

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cally characterized to confirm that nearly 100% of the CH2Cl2 molecules were present (Figure S2 in Supporting Information). It should be noted that the o-ClPh groups of [Ru(1)2] of 1′, which were disordered in 1-dry, become ordered again as 1, whereas those of [Ru(2)2] remain disordered through the entire process of 1 f 1-dry f 1′ (Figure 2). Important bond distances and angles of 1′ are listed in Table 1. No significant difference is observed among the series. The charge distribution in the change from 1 f 1-dry f 1′ is essentially invariant: The average Ru-Oeq distances for the [Ru(1)2] and [Ru(2)2] units are 2.029 and 2.039 Å in 1-dry and 2.036 and 2.043 Å in 1′, being intermediate between values for [Ru2II,II] and [Ru2II,III] as well as 1, and the F value estimated from the TCNQ(MeO)2 moiety using the Kistenmacher relationship is -1.28 and -1.80 for 1-dry and 1′, respectively. The lack of oxidation state conversion in going from 1 f 1-dry f 1′ was also confirmed by solid state diffuse reflectance spectra of these compounds (Figure S3 in Supporting Information), in which three important bands, the π-π* band of TCNQ(MeO)2• - at ca. 1.5 eV, the charge-transfer band of [Ru2II,II] f TCNQ(MeO)2 at ca. 0.8 eV, and the intervalence charge-transfer band between [Ru2II,II] and [Ru2II,III]+ at energies less than 0.8 eV, were continuously observed throughout the series. Field-cooled dc magnetic susceptibility (FCM) data were collected on a freshly harvested polycrystalline sample of 1 in the temperature range of 1.8-300 K at several fields (Figure 3). The χT value of 1.80 cm3 · K · mol-1 at 300 K (at 1 kOe; Figure 3a) is less than the spin-only value of 2.00 cm3 · K · mol-1 for a set of two S ) 1 spins with g ) 2.00 for isolated [Ru2II,II] units as calculated on the basis of no redox reaction. This result not only indicates that the charge transfer from the [Ru2II,II] unit to the TCNQ(MeO)2 moiety occurs in 1 but also that a significant coupling of magnetic centers occurs through TCNQ(MeO)2• - within and between layers even at high temperatures (vide infra). The observed lower χT values at high temperatures are attributed to the following three reasons. The first is the large anisotropy of [Ru2II,II] and [Ru2II,III] units with D ≈ 400 K (S ) 1) and D ≈ 100 K (S ) 3/2), respectively. The second one is that antiferromagnets (such as 1; vide infra) in this type of system have strong interlayer antiferromagnetic interactions even at high temperatures (vide infra).12 The last one is that it is not obvious whether the spin arrangement in a layer is ferromagnetic or ferrimagnetic because of the above two reasons. Upon decreasing the temperature, the χT value gradually increases in the high temperature region and then drastically increases at around 80 K to reach 243 cm3 · K · mol-1 at 62 K followed by a decrease to 9.50 cm3 · K · mol-1 at 1.8 K. As expected from this χT behavior, the χ value at 1 kOe exhibits a rapid increase at ca. 80 K without any decrease being observed over the entire temperature range (Figure 3a). Measurements

Reversible Magnetism in a Robust Layered [Ru2]2TCNQ

Figure 3. Temperature dependence of χ and χT measured at 1 kOe (a)

and field-cooled magnetization curves measured under different external fields less than 1 kOe for 1 (b). The solid line is a guide for the eye.

Figure 4. Temperature dependence of the ac susceptibilities χ′ (in-phase) and χ′′ (out-of-phase) of 1 at zero dc field and in a 3 Oe ac oscillating field.

at an external field less than 300 Oe, however, show a peak around 70-75 K (Figure 3b), owing to a spin flip from an antiferromagnetic (AF) phase to a paramagnetic (P) phase. To obtain more details of the spin ordering near this temperature, temperature dependence of the ac susceptibility was measured under a zero dc field and a 3 Oe oscillating field. The in-phase susceptibility (χ′) shows a sharp peak at 75 K without frequency dependence (Figure 4), and there is no anomaly in the out-ofphase susceptibility (χ′′), indicating the occurrence of an antiferromagnetic phase transition with TN ) 75 K. We note that a small, broad peak for χ′ was also observed at ∼35 K, which is due to defects caused by a minimal loss of solvent (vide infra). This spin flip phenomenon can also be observed in the field dependence of the magnetization (Figure 5a); the initial magnetization experiences a spin flip that that can be detected as a peak in a dM/dH plot (Figure 5b). Ultimately, these data lead to an H-T phase diagram for 1 as shown in Figure 6 characteristic of metamagnetism.15 Nevertheless, this

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Figure 5. (a) Field dependence of the magnetization measured at various temperatures between 1.8 and 100 K and (b) dM/dH vs H plots for the virgin magnetization of 1. Inset of (a): temperature dependence of the coercive field (Hc).

Figure 6. H-T phase diagram for 1, where AF and P represent the

antiferromagnetic and paramagnetic phases, respectively. TN (75 K) was determined from the χ′ versus T data at H ) 0 (Figure 4). The dashed line is a guide for the eye.

metamagnetic behavior is unusual; after the material achieves a P-phase, 1 becomes a field-induced canted antiferromagnet with a large coercivity up to 1.6 T at 1.8 K (Figure 5a). The coercivity disappears at ca. 80 K (inset of Figure 5a).16 The details of the M-H hysteresis will be described below. The sample of 1 was gradually dried in situ in a SQUID apparatus by repeating the process of standing for 3 h at 300 K with venting followed by cooling to 100 K to measure the ac susceptibility from 100 to 1.8 K and an MH curve at 1.8 K (the time profile for the measurements is given in the inset of Figure 7). Figure 7 displays the variation of temperature dependence of ac susceptibilities (1 Hz) as the process is repeated 8 times (15) Considering the small χT value at 300 K and the value of the saturation magnetization in M vs H plots, the P-phase for 1 may be associated with a spin canted mode. The spin flop (SF) phase was not detected in measurements performed in this work. J. AM. CHEM. SOC.

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Figure 8. In situ FCM, RM, and ZFCM for the in situ sample after 21 h (corresponding to 1-dry), where a field of 5 Oe was applied for FCM and ZFCM.

Figure 7. Variation of 1 Hz ac susceptibilities χ′ (top) and χ′′ (bottom) (zero dc field and 3 Oe ac oscillating field) during an in situ desolvation process, where the times in the legend represent integrated times at 300 K (each step has a holding time of 3 h, as the time profile indicates in the inset). Detailed views of the initial data and after 3 h are also shown in the inset.

(ultimately, the sample was kept for 21 h at 300 K). As the process of desolvation proceeds, the peak in χ′ at 75 K () TN) for 1 decreases and a new maximum in χ′ appears in the range 50-60 K with a distinct signal being observed in χ′′. This new feature appears to be a result of a shift in the broad anomaly peak at 35 K observed in 1 (inset of Figure 5; it is therefore concluded that the broad peak in 1 is a result of defects associated with the desolvation). Whereas this peak is finally saturated after 21 h at 300 K, conversely, the χ′ feature at 75 K that disappeared after 9 h at 300 K reappears and increases along with the appearance of a χ′′ signal. The aforementioned results are interpreted as follows: The χ′ maximum at 50-60 K represents a spontaneous magnetization that involves a fixing of the ferromagnetically ordered domains with a χ′′ signal that begins to appear at ca. 75 K in a gradual fashion. Such a slow increase in χ′′ has often been observed for spin-glass-like materials or magnets with anisotropic spins.17,18 Indeed, the present system is composed of anisotropic spins. Meanwhile, the small anomaly at 75-80 K that appeared after 21 h is probably due to the effect of some defects. To further probe this process, FCM, remnant magne(16) (a) Kurmoo, M. Philos. Trans. R. Soc. 1999, 357, 3041. (b) Kurmoo, M.; Kumagai, H.; Green, M. A.; Lovett, B. W.; Blundell, S. J.; Ardavan, A.; Singleton, J. J. Solid State Chem. 2001, 159, 343. (c) Kumagai, H.; Keppert, C. J.; Kurmoo, M. Inorg. Chem. 2002, 41, 3410. (d) Kurmoo, M.; Kumagai, H.; Hugues, S. M.; Kepert, C. J. Inorg. Chem. 2003, 42, 6709. (e) Numata, Y.; Inoue, K.; Buranov, N.; Kurmoo, M.; Kikuchi, K. J. Am. Chem. Soc. 2007, 129, 9902. (f) Ishii, N.; Okamura, Y.; Chiba, S.; Nogami, T.; Ishida, T. J. Am. Chem. Soc. 2008, 130, 24. (17) Miyasaka, H.; Nakata, K.; Lecren, L.; Coulon, C.; Nakazawa, Y.; Fujisaki, T.; Sugiura, K.; Yamashita, M.; Cle´rac, R. J. Am. Chem. Soc. 2006, 128, 3770. (18) Coronado, E.; Gala´n-Mascaro´s, J. R.; Martı´-Gastaldo, C.; Ribera, A.; Palacios, E.; Castro, M.; Burriel, R. Inorg. Chem. 2008, 47, 9103. 11948

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Figure 9. Field dependence of the magnetization at 1.8 K for 1, the samples

produced in the in situ desolvation process, and 1′.

tization (RM), and zero-field-cooled magnetization (ZFCM) were measured for the in situ sample after 21 h (i.e., corresponding to 1-dry) at 5 Oe (Figure 8). The ZFCM leads to a peak at 56 K, in good agreement with the ac data, but completely follows FCM above 75 K. In addition, RM disappears at this temperature. These data are in accord with the conclusion of a gradual growth of ferromagnetically ordered domains, a process that begins at ca. 75 K and fixes at 56 K.19 The M versus T data for our new material indicate that, with gradual elimination of the CH2Cl2 solvent of crystallization at room temperature, the magnetic properties of the present compound are tuned from an antiferromagnet for 1 to a ferromagnet for 1-dry, with intermediate species being possible wherein both domains are present as mixtures. Field dependence of the magnetization of all in situ samples was measured at 1.8 K (Figure 9) immediately following the measurements of the ac data (Figure 7) and M versus T data (Figure 8). For a fresh sample of 1, the initial magnetization curve indicates a flip at 1.5 T to transfer to the P-phase and reaches Ms ) 1.43 µB at 7 T, showing a metamagnetic transition typically observed for anisotropic antiferromagnets. Interestingly, this saturated magnetization does not follow the initial process and results in a magnetization at zero field (remnant magnetization) and a field-dependent hysteresis with a coercivity of Hc ) 1.6 T; these data represent that of a field-induced cantedantiferromagnet (Figures 5 and 9). Such a large coercivity implies a hard magnet, a result that has been reported in the literature for other 2D network compounds.12,16,20 This phe(19) Kurmoo, M. Chem. Soc. ReV. 2009, 38, 1353. (20) Motokawa, N.; Oyama, T.; Matsunaga, S.; Miyasaka, H.; Yamashita, M.; Dunbar, K. R. CrystEngComm 2009, 11, 2121.

Reversible Magnetism in a Robust Layered [Ru2]2TCNQ

Figure 10. Temperature dependence of χ and χT of 1-dry produced in

the in situ process (after 21 h) measured at 1 kOe. Inset: field-cooled magnetization curves measured under low external fields. The solid line is a guide for the eye.

nomenon is due to domain-wall triggers associated with the origin of interlayer antiferromagnetic interactions (between layers of solvated segments) rather than intralayer triggers such as large anisotropy arising from the [Ru2] units. It should be pointed out that this coercivity for 1 disappears even when the sample is left for several minutes at room temperature. The initial magnetization of partially dried and 1-dry samples still display features of a hard magnet: a spin flip is observed at 1 T. Nevertheless, the saturated magnetization becomes much higher than that observed for the fresh sample 1, reaching Ms ) 2.5 µB at 7 T (with release of CH2Cl2 the saturated magnetization gradually increases, which is most likely due to small areas of canted spin domains). Even in partially dried samples (and 1-dry) the remnant magnetization is preserved until close to H ) 0 but with no coercivity; therefore these materials are basically identical soft-ferromagnets (note that butterfly-type hysteresis loops are observed at low fields in partially dried samples, which become more narrow with increasing degree of desolvation). This phenomenon is akin to a magnetic avalanche.21 It should be emphasized that, even in the case of a small loss of CH2Cl2, which would create only a small fraction of ferromagnetically ordered domains in a crystal as observed from the ac data in Figure 7, the information of the minor segments of the ferromagnetically ordered domain dictates the state of the magnetism after the P-phase is reached in applied fields. This is quite unusual and very interesting because despite the fact that the desolvation process is expected to increase the number of defects generally capable of acting as areas of pinning for domain walls, the domain walls are easy to move in this system. Figure 10 shows χ and χT plots for 1-dry estimated from FCM data at 1 kOe as a function of temperature. At an external field of 1 kOe, the behavior is very similar to what was found for 1 (Figure 3a), but the behavior at low fields is completely different from that of the antiferromagnet 1 (Figure 8 and inset of Figure 10). There is no flip of spins from the AF-phase to the P-phase and the χT value at 300 K is 3.06 cm3 · K · mol-1, larger than the value observed for 1. Assuming that the intralayer magnetic nature of 1 is preserved in 1-dry, this difference hints at the existence of strong interlayer antiferromagnetic interactions in 1 even at 300 K. The frequency dependence of ac susceptibilities was measured on a sample of 1-dry under a zero dc field and a 3 Oe oscillating field (Figure 11; note that these (21) Minguet, M.; Luneau, D.; Lhotel, E.; Villar, V.; Paulsen, C.; Amabilino, D. B.; Veciana, J. Angew. Chem., Int. Ed. 2002, 41, 586.

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Figure 11. Temperature dependence of the ac susceptibilities χ′ (in-phase)

and χ′′ (out-of-phase) of 1-dry produced in the in situ process (after 21 h) at zero dc field and in a 3 Oe ac oscillating field.

Figure 12. Field dependence of the magnetization of 1-dry produced in

the in situ process (after 21 h) measured at various temperatures between 1.8 and 100 K, where the initial magnetization curves are omitted for the sake of clarity.

data were measured after the M vs H data.). Slight frequency dependence is observed even though the peak of χ′ is fixed, in accord with slowly growing ferromagnetically ordered domains being present as concluded from the FCM, RM, and ZFCM measurements (Figure 8). Finally, M versus H data were measured at several temperatures up to 100 K (Figure 12). The “softness” of the magnets was preserved up to 100 K after applying high fields. The dried sample 1-dry returns back to the solvated form of 1′ with nearly 100% occupancy for the CH2Cl2 molecules per formula unit only by allowing the sample to stand in a CH2Cl2 atmosphere during 72 h or more; complete conversion to 1 is not achieved at such a mild condition because of the presence of small defects. As shown in Figure 13, the spin flip phenomenon for the metamagnetic nature observed in 1 was recovered, but the χT value at 300 K is 2.65 cm3 · K · mol-1 (1 < 1′ < 1-dry), which implies the presence of small defects caused by the desolvation/desolvation process rather than incomplete reversibility of solvation. Indeed, in the temperaure dependence data of the ac susceptibilites, a sharp and strong maximum in χ′ was observed at 75 K, corresponding to TN, with a broad and weak peak involving χ′′ signals at 40-80 K (Figure 14). Also in the M-H curve at 1.8 K, the value of Ms of 1′ is a little higher than that observed for 1, but the coercivity is recovered to the same value as 1 (Figure 9). Thus, magnetic properties are nearly reversible between 1 and 1-dry (the temperature dependence of M-H curves and a H-T phase diagram derived from the data of M vs T and dM vs dH for 1′ are provided in Figures S4 and S5, respectively, in Supporting J. AM. CHEM. SOC.

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Motokawa et al.

Figure 13. Temperature dependence of χ and χT of 1′ measured at 1 kOe.

Inset: field-cooled magnetization curves measured under low external fields. The solid line is a guide for the eye.

Figure 14. Temperature dependence of the ac susceptibilities χ′ and χ′′ of 1′ at zero dc field and 3 Oe ac oscillating field. Inset: close-up view of χ′′.

Information). From the structural point of view, very slight changes of the interlayer environment result in a dramatic magnetic modification, although only a 1.2 vol % of volume change occurs between 1 and 1-dry. It is proposed that the order/ disorder of o-ClPh groups in [Ru(1)2] is mainly responsible for tuning the magnetic properties. It is possible that the disordered form in [Ru(1)2] results in structural/magnetic fluctuations, which not only disturb the antiferromagnetic alignment of interlayer spins but also trigger the pinning of domain walls. Concluding Remarks

The present compound is exquisitely sensitive to slight changes of structure that alter the magnetic properties from an antiferromagnet for CH2Cl2-solvated 1 at H ) 0 to a cantedantiferromagnet (hard magnet) under applied fields and finally to a soft ferromagnet for partially dried or dried samples (1dry). The latter samples revert to a CH2Cl2-solvated phase (1′) by exposure of 1-dry to CH2Cl2 vapor at room temperature. Essentially, this material exhibits a robust framework with an order/disorder in a substituent group that leads to flexible magnetic ground states dependent on the degree of solvation. Thus, the present compound revealed a new concept for reversible magnetism in which a trigger as subtle as a structural fluctuation, in this case order/disorder of a ligand substituent, is crucial for deciding the magnetic properties. These results are quite different from the known cases of reversible changes in magnetism for materials that undergo major structural changes effected by interstitial solvent loss. Experimental Section Synthesis of 1. All synthetic procedures were carried out under anaerobic conditions. The starting material [Ru2(O2CPh-o-Cl)411950

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(THF)2] was prepared by adaptation of a literature procedure.22 A CH2Cl2 solution (20 mL) of [Ru2(O2CPh-o-Cl)4(THF)2] (97 mg, 0.1 mmol) was separated into 2 mL portions and placed in narrow diameter sealed glass tubes (φ ) 8 mm). Then 2 mL portions of nitrobenzene solution (20 mL) of TCNQ(OMe)2 (13 mg, 0.05 mmol) were carefully placed onto the CH2Cl2 layers to allow for slow diffusion to occur. The glass tubes were left undisturbed for 1 week or more to yield block-shaped dark-green crystals of 1. Yield: 74%. Elemental analysis (%) calcd for 1 C71H42Cl10N4O18Ru4: C 42.68, H 2.12, N 2.80. Found: C 42.90, H 2.29, N 3.05. IR (KBr): ν(CtN), 2193, 2158, 2106 cm-1. General Physical Measurements. Infrared spectra were measured on KBr disks with a Jasco FT-IR 620 spectrophotometer. TG-DTA data for monitering the removal of interstitial solvent molecules in the bulk preparation of 1-dry were conducted on a Shimadzu DTG-60H instrument with a temperature sweep rate of 5 °C/min. Magnetic susceptibility measurements were conducted with a Quantum Design SQUID magnetometer (MPMS-XL) in the temperature and dc field ranges of 1.8 to 300 K and -7 to 7 T. AC measurements were performed at various frequencies ranging from 1 to 1488 Hz with an ac field amplitude of 3 Oe. Polycrystalline samples embedded in liquid paraffin were measured except for the SQUID in situ preparation of 1-dry. Experimental data were corrected for the sample holder and liquid paraffin and for the diamagnetic contribution calculated from Pascal constants.23 Magnetic Measurements and SQUID in Situ Preparation of 1-dry. The magnetic measurements for 1 and 1′ were first carried out using freshly prepared samples embedded in liquid paraffin to prevent the elimination of crystallization solvent (CH2Cl2) under a reduced pressure. Magnetic measurements for partially dried samples prepared in situ in the SQUID were carried out by the following procedures. The freshly harvested sample of 1 in a gelatin capsule without any coating agent was put into a SQUID and immediately cooled to 100 K under reduced pressure, at which stage even the initial sample is not a fresh sample but is a partially dried sample. Ac magnetic susceptibilities and M-H curves for this sample were measured in the temperature range of 1.8-100 K, and then the sample was heated to 300 K and kept at this temperature for 3 h. This procedure was repeated (8 times) until no significant change was observed. Crystallography. Single crystals with dimensions of 0.25 × 0.23 × 0.04 mm3 for 1, 0.15 × 0.13 × 0.05 mm3 for 1-dry, 0.15 × 0.14 × 0.03 mm3 for 1′, 0.18 × 0.16 × 0.10 mm3 for [Ru2II,II(O2CPho-Cl)4(THF)2] · 2THF, and 0.12 × 0.08 × 0.03 mm3 for [Ru2II,III(O2CPho-Cl)4(THF)2]BF4 · THF were mounted on cryo-loops or glass fibers using Nujol and cooled by a stream of cooled N2 gas. All measurements were made on a Rigaku Saturn CCD area detector with a graphite monochromated Mo KR radiation (λ ) 0.71070 Å). The structures were solved by direct methods (SHELXL 97, SIR 97, and SIR 92)24 or heavy-atom Patterson methods25 and expanded using Fourier techniques (DIRDIF99).26 Most nonhydrogen atoms in the main part of the structure were refined anisotropically, while the rest (as crystallization solvents) were (22) Furukawa, S.; Kitagawa, S. Inorg. Chem. 2004, 43, 6464. (23) Boudreaux, E. A.; Mulay, L. N. Theory and Applications of Molecular Paramagnetism; John Wiley and Sons: New York, 1976; p 491. (24) (a) Sheldrick, G. M. SHELXL 97; University of Gottingen: Gottingen, Germany, 1997. (b) Altomare, A.; Burla, M.; Camballi, M.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115. (c) Altomare, A.; Burla, M. C.; Camballi, M.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994, 27, 435. (25) PATTY: Beurskebs, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF program system, Technical Report of the Crystallography Laboratory; University of Nijmengen: Nijmengen, The Netherlands, 1992. (26) DIRDIF99: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-99 Program System, Technical Report of the Crystallography Laboratory; University of Nijmengen: Nijmengen, The Netherlands, 1999.

Reversible Magnetism in a Robust Layered [Ru2]2TCNQ

refined isotropically because of the presence of disorder. Hydrogen atoms were introduced as fixed contributors. Full-matrix leastsquares refinements on F2 were based on observed reflections and variable parameters, and converged with unweighted and weighted agreement factors of R1 ) Σ|Fo| - |Fc|/Σ|Fo| (I > 2.00σ(I)), and wR2 ) [Σw(Fo2 - Fc2)2/Σw(Fo2)2]1/2 (all data). All calculations were performed using the CrystalStructure crystallographic software package.27 These data have been deposited as CIFs at the Cambridge Data Centre as supplementary publication nos. CCDC769038 for 1, 769037 for 1-dry, 769039 for 1′, 770525 for [Ru2II,II(O2CPh-o-Cl)4(THF)2] · 2THF, and 770524 for [Ru2II,III(O2CPho-Cl)4(THF)2]BF4 · THF. Copies of the data can be obtained free of charge by application to CCDC, 12 Union Road, Cambridge CB21EZ,UK(fax:(+44)1223-336-033;email:[email protected]). Crystal Data for 1. C71H42N4O18Cl10Ru4, FW ) 1997.94, triclinic P-1 (No. 2), T ) 103 ( 1 K, λ(Mo KR) ) 0.71075 Å, a ) 10.18970(10) Å, b ) 11.8946(2) Å, c ) 15.8515(3) Å, R ) 83.299(3)°, β ) 86.941(3)°, γ ) 80.846(3)°, V ) 1882.63(5) Å3, Z ) 1, Dcalc ) 1.762 g · cm-3, F000 ) 986.00, 2θmax ) 55.0°. Final R1 ) 0.0467 (I > 2.00σ(I)), R ) 0.0519 (all data), wR2 ) 0.1333 (all data), GOF ) 1.104 for 495 parameters and a total of 12441 reflections, 6388 unique (Rint ) 0.014). µ ) 12.132 cm-1. Fmax ) 2.19 e/Å3 and Fmin ) -1.63 e/Å3. Crystal Data for 1-dry. C70H40N4O18Cl8Ru4, FW ) 1913.01, triclinic P-1 (No. 2), T ) 103 ( 1 K, λ(Mo KR) ) 0.71075 Å, a ) 10.024(3) Å, b ) 12.034(4) Å, c ) 15.707(5) Å, R ) 84.078(10)°, β ) 85.712(11)°, γ ) 79.834(9)°, V ) 1851.9(10) Å3, Z ) 1, Dcalc ) 1.715 g · cm-3, F000 ) 944.00, 2θmax ) 55.0°. Final R1 ) 0.0485 (I > 2.00σ(I)), R ) 0.0643 (all data), wR2 ) 0.1417 (all data), GOF ) 1.079 for 488 parameters and a total of 12420 reflections, 6340 unique (Rint ) 0.022). µ ) 11.595 cm-1. Fmax ) 2.14 e/Å3 and Fmin ) -0.80 e/Å3. Crystal Data for 1′. C71H42N4O18Cl10Ru4, FW ) 1997.94, triclinic P-1 (No. 2), T ) 103 ( 1 K, λ(Mo KR) ) 0.71075 Å, a ) 10.1872(15) Å, b ) 11.8862(17) Å, c ) 15.811(2) Å, R ) 83.433(3)°, β ) 86.957(3)°, γ ) 80.850(3)°, V ) 1876.5(5) Å3, Z ) 1, Dcalc ) 1.768 g · cm-3, F000 ) 986.00, 2θmax ) 55.0°. Final R1 ) 0.0518 (I > 2.00σ(I)), R ) 0.0603 (all data), wR2 ) 0.1573 (27) CrystalStructure 3.15: Crystal Structure Analysis Package; Rigaku and Rigaku/MSC: The Woodlands, TX, 2000-2002.

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(all data), GOF ) 1.007 for 518 parameters and a total of 15143 reflections, 8200 unique (Rint ) 0.016). µ ) 12.172 cm-1. Fmax ) 3.19 e/Å3 and Fmin ) -1.41 e/Å3. Crystal Data for [Ru2II,II(O2CPh-o-Cl)4(THF)2] · 2THF. C44H48O12Cl4Ru2, FW ) 1112.81, orthorhombic Pbca (No. 61), T ) 93 ( 1 K, λ(Mo KR) ) 0.71075 Å, a ) 9.151(4) Å, b ) 20.914(10) Å, c ) 23.367(18) Å, V ) 4472(4) Å3, Z ) 4, Dcalc ) 1.653 g · cm-3, F000 ) 2256.00, 2θmax ) 50.0°. Final R1 ) 0.0400 (I > 2.00σ(I)), R ) 0.0424 (all data), wR2 ) 0.0938 (all data), GOF ) 1.092 for 281 parameters and a total of 28317 reflections, 3901 unique (Rint ) 0.030). µ ) 9.763 cm-1. Fmax ) 0.80 e/Å3 and Fmin ) -0.74 e/Å3. Crystal Data for [Ru2II,III(O2CPh-o-Cl)4(THF)2]BF4 · THF. C40H40O11Cl4F4BRu2, FW ) 1127.50, monoclinic P21/n (No. 14), T ) 93 ( 1 K, λ(Mo KR) ) 0.71075 Å, a ) 14.8115(19) Å, b ) 15.9646(19) Å, c ) 18.929(2) Å, β ) 106.6646(16)°, V ) 4288.0(9) Å3, Z ) 4, Dcalc ) 1.746 g · cm-3, F000 ) 2260.00, 2θmax ) 50.0°. Final R1 ) 0.0518 (I > 2.00σ(I)), R ) 0.0527 (all data), wR2 ) 0.1220 (all data), GOF ) 1.142 for 596 parameters and a total of 26581 reflections, 7453 unique (Rint ) 0.025). µ ) 10.302 cm-1. Fmax ) 2.67 e/Å3 and Fmin ) -1.14 e/Å3. Acknowledgment. The authors acknowledge Ms. Miho Takemura (Tohoku University) for measurements of powder reflection spectra. This work was supported by a Grant-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology (Japan) and The Asahi Glass Foundation (H.M.). N.M. thanks the JSPS Research Fellowships for Young Scientists for financial support. K.R.D. thanks the National Science Foundation (CHE0957840) for support of this work. Supporting Information Available: X-ray crystallographic files in CIF format for 1, 1-dry, 1′, [Ru2II,II(O2CPh-oCl)4(THF)2] · 2THF, and [Ru2II,III(O2CPh-o-Cl)4(THF)2]BF4 · THF, bond distances in [Ru2II,II(O2CPh-o-Cl)4(THF)2] · 2THF and [Ru2II,III(O2CPh-o-Cl)4(THF)2]BF4 · THF, and additional figures. This material is available free of charge via the Internet at http:// pubs.acs.org. JA102412G

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